Not Applicable
Not Applicable
1. Technical Field
This invention relates to a battery case, cover, and feedthrough and more particularly to a method and apparatus for providing a sealed battery having a lightweight case.
2. Background Art
Battery cases typically require a conductive pin that feeds into the case through a dielectric material that insulates the pin from the conductive case wall. It is generally critical that the feedthrough be hermetically sealed.
Techniques are known for forming a hermetic seal between a metal pin of high melt point material and a ceramic cylinder surrounding the pin. Moreover, an annular metal collar of high melt point material can be hermetically sealed around the ceramic cylinder.
It is often desirable to be able to form a battery case of lightweight low cost material, such as aluminum. Aluminum can be deep drawn and has a density of 2.7 g/cm3 as compared with the density of stainless steel of 7.8 g/cm3. Unfortunately, aluminum melts at a temperature lower than the temperatures normally required to fabricate and install the aforedescribed ceramic-metal feedthrough structure in the case. For example, the fabrication of the aforedescribed structure typically requires the application of a temperature of about 800xc2x0 C. or more to form a hermetic seal between two high melt point metals and/or between a high melt point metal and a ceramic cylinder. Such an elevated temperature could destroy a case formed of aluminum, which melts just above 600xc2x0 C.
The present invention is directed to an improved case/feedthrough construction enabling the use of a low melt point case material, e.g., aluminum, in conjunction with a ceramic-metal feedthrough subassembly that requires the application of a high temperature to form a hermetic seal.
In accordance with the invention, a case cover comprising a layer of high melt point material and a layer of low melt point material is used to respectively seal to a high melt point collar on the feedthrough subassembly and a low melt point case.
More particularly, in accordance with a preferred embodiment, a case cover is formed of clad metal comprised of a layer of high melt point material, e.g., stainless steel or titanium, and a layer of low melt point material, e.g., aluminum. A feedthrough hole is formed through the cover. The feedthrough subassembly annular collar is aligned with the hole and hermetically sealed to the clad metal high melt point layer using a high temperature welding process.
The clad metal low melt point layer, e.g., aluminum, can be laser welded to the aluminum case at a lower temperature to form a hermetic seal.
In another embodiment, the feedthrough does not have an annular metal collar, and both layers of cladding can withstand the temperatures required for sealing the dielectric material, e.g. glass, to the cover.